Polyvinyl alcohol gels and photographic silver halide emulsions containing berylliumcompounds



Patented Mar. 2, 1954 GRAPHIC SILVER HALIDE.

EMULSIONS CONTAINING BERYLLILUM. .CUMEOUNDST.

Donald E. Sargent, Eastom, Pa and 101x110; Bail'ar lra- Urbano, Ill.,..assignors to General; Aniline=*&w Gorporation,,.New York, N'.. Y.,, amorporation of Delaware No. Drawing: Application June" 2'4; 19:49, Seriat No. for-,2

l3- Glaims.

The resent invention relates to the perparaoi polyvinyl alcoholgels and to such gelswhion constitute, inter alia, colloids useful. in photography.

is Welt known, natm aii gelatihsare almost universally employed as the protective colloid in photographic: emulsions; Despite this fact, the'se. natural products have-seriousshortcornings which have kindleda'strong desire in the art for the creation ofgelatin substitutes free from the ohjeetionsto gelatin.

Amongthe shortcomings of gelatin are variability in physical properties and in chemical cont position which lead to variations in the physical and photographic propertiesiof the finished photographie emulsion andto variations in the susceptiioility of the silver halides thereof to sensitizing and desensitizing" substances, developing agents, and the like: brittleness when dryso that photographic products carrying emulsion layers containinggelatincrackrather easily; particularlyprinting" papers soprepared; low resistance to the action o-fbacteri'a and molds; susceptibility to the action of strongly alkaline reagents; low melting; points when wet, making it'necessary to-procsee the photographic material at relatively low temperature, e., on theorder-of 1-5 to 25 6;

Any useful gelatin substitute shouldpossess' the gel-forming and protective colloid action of'gelatin but be free from the aforementioned disadvantages. Such a, material should have fairly constant physical and chemical properties allowing emulsions ofconstant properties" to" :be prepared, should be, superior to gelatin as afilmformingymateri'al, anct should not be attacked by bacteriaormolds.

Polyvinyl alcohol; isa highmolecular weight, water soluble polymer which yields tough transparent films when its aqueous solutions are dried; It'i's readily available and the chemical and physical properties of any given grade arefairly constant; Commercial-1y itis manufactured by hydrolyzingpolyvinyl acetate partially or completel-yto give a: variety of products: The term polyvinyl alcohol as. herein used also includes water-soluble hydrolyzed polyvinyl esters having apoiyvinyl ester content of lessthe-n25 the remainder" being poly-vinyl alcohol The structureof a completely hydrolyzed; polyvinyLester-may be represented schematically by the following 60' formula:

v /C.Er fcge. fCHe.

on. on (EH;

' n' on on 2 It will? noted trom; this formula thatalterhate. carbon: atomsare substituted 'by hydroxyl groups. It is to these. hydroxyl groups. that. the water solubility of the product is: attributable;

: There. is interaction(hydrogen bonding.) between these. hydroxyl groups and. water and between-the hydroxyl groups of adjacent chains sothat the solutions in water" show an appreciable viscosity. Unfortunately, however, these forces arenotsuificient vper se to cause the productto gel on stand:- lng at. room temperature or upon cooling.

Considerable work has been done in an eitortto convert polyvinyl alcohol into amaterial which would possess. the properties. aforesaid and would serve as an effective gelatin. substitute. For the most part, this workwas predicated upon the-use oforganic compound'sas the gelling agents. Q ne exceptionis provided USP 2,376,371 which suggests the employment of boron compounds, such as borie. acid, and the like, for gelling polyvinyl alcohol. This. action was to be expected for the reason that it is known that boric-acid and similar boron derivatives undergo ester or com-plexfoiunation with polyhydro xy compounds, such as'gl-ycerine; carbohydrates; and the like (see for example the bottom of page 1699 of "Organic Chemistry by Gilman, vol. II, second edition). It could therefore be" assumed that the' same action would be portrayed in connection with polyvinyl alcohol and that such action could easily lead to a crosslinked or gelled structure.

We have now found,:suprisingly, that beryliium compounds possess theabiIi-tyto-ge1 po1yvihy1 alcohol in conjunction with a basic material man evengreater degree than do boron compounds,

such as boric acid despite themarked difference between these two types of compounds. Thecl-ifv ferenceis illustrated by fact that it is well known that boron is distinctly non-metallic (see for ex ample, Lati'mer and Hildebrand, Reference Book of'lhorganic Chemistry; The McMillan Company; New York, I940, page 80, second paragraph) while beryl-lium is classified as ametal- (ihi'd, page 57). Because of this, the hydroxideof boron B [301E191 is an acid while the hydroxide of herylliumiBeEOHlzl is a base; Furthermore; boron never appears "as'the- B oationwhen'its compounds are dissolved in water, but always oc curs" in ananion comhi'nation" with another non 'metal such as oxygen tort example th B021- and B4O'r. anions. By way of'contrast beryl l-iunr compounds in. aqueous solution; readily yield the.- Be++ cation which is typical of-ithe behavior ofisaltsrofthemetalsi ltzmay alsoa be: noted that. beryllium appears:

Ii the same group of the periodic system with magnesium, calcium, strontium, barium, zinc and cadmium. Like the hydroxide of beryllium, the hydroxides of these other metallic elements exhibit the characteristics of bases. Because of this, it was to be presumed that the gelling action of beryllium compounds would be comparable to that of similar compounds of the metalsmost closely related thereto, i. e., of those which have the same valence and appear in the same group of the periodic system. Investigation has shown however that aqueous solutions of the salts of magnesium, calcium, strontium, barium, zinc and,

cadmium when added to an aqueous solution of polyvinyl alcohol, followed by addition of a basic material effect very little or no gelling action on the polyvinyl alcohol. In facewith magnesium and calcium compounds, the hydroxides may precipitate. With zinc and cadmium compounds, on the other hand, while, semi-opaque heterogeneous masses are formed which may precipitate and which exhibit few of the desirable characteristics of a clear tough homogeneous gel. It was therefore suprising, that solutions of beryllium compounds, unlike those of its congeners form gels with polyvinyl alcohol upon treatment with a basic material.

Furthermore it is well known that compounds of beryllium are often similar to compounds of aluminum in both physical and chemical properties. Never-the-less the above-noted gelling action of beryllium compounds is not shared by aluminum compounds.

The beryllium compound-polyvinyl alcohol gel are even stronger than those formed with boron compounds. This is probably attributable to the fact that in many cases the boron compounds, being derived from a trivalent element, form structures which are too highly cross-linked and are therefore rigid and too easily shared, whereas the beryllium compounds, being derived from an element which is only divalent, form more elastic gel structures. Our discovery, which as noted, is quite unexpected, involves the preparation of colorless gels having a very high mechanical strength and eminently suitable for the preparation of photographic emulsions by adding to polyvinyl alcohol solution a solution of a water soluble beryllium compound followed by treatment with a basic material. This gelling action may be due to the formation of beryllium hydroxide in situ from the beryllium compound and the reaction of the hydroxide with the chain-like molecules of the polyvinyl alcohol. It is to be understood, however, that this explanation is. merely given as a possible illustration of the mechanism of the reaction and is not being submitted as an actual indication of the reaction which takes place.

Clear, tough, high melting polyvinyl alcohol gels containing soluble beryllium compounds and a basic substance and the preparation of such gels constitute the purposes and objects of the present invention.

The gels contemplated herein are produced by adding to a water solution of polyvinyl alcohol, a water soluble compound'of beryllium andthen modifying the pH of the resulting mixture by treatment w th a water soluble basic material. Such treatment may be efiected in various ways. One method involves the addition to the mixture of the polyvinyl alcohol and the beryllium compound, a solution of a watersoluble basic material such as sodium hydroxide, potassium by". droxide, sodium carbonate, ammonia, ammonium 4 carbonate, or the like. Alternatively, the solution of the polyvinyl alcohol and beryllium compound may be coated on a suitable support and gelation effected by fuming the .coating' with a volatile base such as ammonia or an organic amine such as methylamine, ethylamine, ethylenediainine, or the like, or by dipping the coated I support into an aqueous solution of a base, either be used for the intended purpose.

' alcohol used. For the best results it is preferred to employ the beryllium compound in an amount ranging from about 1 to 5% by weight of the polyvinyl alcohol. The exact amount used may depend upon the molecularweight of the polyvinyl alcohol used and the properties desired in the finished product.

The aforesaid polyvinyl alcohol-beryllium compound complexes may be conveniently employed for the preparation of light sensitive photographic silver halide elements by adding to an aqueous solution of polyvinyl alcohol an alkali metal halide such as sodium bromide, sodium chloride, potassium bromide, potassium chloride, or the like, and precipitating therein a silver halide in a finely dispersed state by the addition of a soluble silver salt such as silver nitrate, while continuously stirring the mass. A water soluble beryllium compound is then added, while stirring, and the resulting composition is coated on a suitable support and gelled by treatment with a basic material as previously outlined. Following the addition of the soluble silver salt, it may be desirable to ripen the emulsion by stirring it at a somewhat elevated temperature, i. e., 35 to 75 C. for a short time or to add auxiliary agents such as sensitizers, desensitizers, ripening agents, dispersing agents, and the like. Flourescing agents such as those described by Sargent in copending applications Serial Nos. 69,841 filed January 7, 1949., now Patent No. 2,582,357; 72,2?7 filed January 22, 1949, now Patent No.2,555,138; and 75,738 filed February 10, 1949, now Patent No. 2,57 ,706, mayalso be added; f It is to be understood that the above proce-. dure need not be strictly followed in producing the light sensitive silver halide elements. Thus beryllium compound may be added prior to the addition of the alkali metal halide and the soluble silver salt with equally good results.

The remarkable gelling action of the beryllium compound is demonstrated by the fact that coatings prepared with the polyvinyl alcohol-beryllium compound complexes are proof against boiling water, whereas if the beryllium compounds are omitted in the preparation of the coatings, solution in boiling water occurs quite readily.

Erample I .f'io parts of a 10% solution of polyvinyl alcohol (Dupont Elvanol 52-22) are added 5' parts of a 10% solution of beryllium nitrate (nanomsmoi with continuous stirring until a homogeneous so- 1y converted into a stifi, colorless, transparent gel which does not dissolve readily in boiling water.

Exampl II To a solution of 125 parts of a polyvinyl alcohol solution (Dupont Elvanol 52-22), is

added, with stirring, a solution of 0.9 part of sodium chloride and 0.5 part of beryllium nitrate dissolved in 25 parts of distilled water. The solution is heated to 50 C. and, in yellow light, a solution of 1.875 parts of silver nitrate in parts of distilled water is added with continuous stirring. After stirring in yellow light for 15 minutes at 15 C., the resulting fluid silver chloride emulsion is coated on a paper base and allowed to cool. The base is then exposed to ammonia fumes until the coating sets to a tough water-insoluble gel. The coating is then dried in the dark. The light sensitive element so prepared is very suitable for making prints from photographic negatives and is not adversely aifected by the usual treating baths as is unmodified polyvinyl alcohol emulsion coatings.

Example 111 The procedure is the same as in Example H excepting that the coating is fumed with methylamine rather than with ammonia. The results obtained are substantially the same as those of Example II.

Example IV The procedure is the same as in Example 11 excepting that the coating is effected on cellulose acetate base and is set by bathing the coating for a short time in a 5% solution of sodium hydroxide, followed by water washing, and drying- Example V The procedure is the same as in Example I excepting that the beryllium nitrate is replaced by an equivalent amount of beryllium chloride. The gel obtained resembles that of Example I.

Ezample VI The procedure is the same as in Example I excepting that the beryllium nitrate is replaced by an equivalent amount of beryllium bromide. A clear, tough gel also results in this case.

It should be understood that the gels formed as herein noted can be used for purposes other than the preparation of photographic products. Such gels may be employed, for example, as thickening and gelling agents in water paints, printing inks, and many other applications where thickening or gelling compositions are required.

Various modifications of the invention will occur to persons skilled in this art, and we therefore do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. The method of preparing a tough, colorless gel which comprises mixing an aqueous solution of polyvinyl alcohol with a water soluble inorganic beryllium salt in a gelling amount and treating the mixture with a water soluble inorganic basic material.

2. The method of preparing a tough, colorless gel which comprises mixing an aqueous solution of polyvinyl alcohol with a water soluble inorganic beryllium salt in a gelling amount and treating the mixture with a basic material selected from the class consisting of water soluble inorganic bases and volatile nitrogenous water soluble organic bases.

3. The process as defined in claim 2 wherein the mixing of the ingredients is effected without heating.

4. The process of producing a light sensitive photographic element comprising a silver halide uniformly dispersed in a tough, colorless gel of polyvinyl alcohol which comprises adding to an aqueous solution of polyvinyl alcohol, an alkali metal halide, adding silver nitrate while continuously stirring the mass, incorporating a water soluble inorganic beryllium salt in a gelling amount, and treating the composition with a basic material selected from the class consisting of water soluble inorganic bases and volatile nitrogenous water soluble organic base.

5. The method of preparing a tough, colorless gel which comprises mixing an aqueous solution of polyvinyl alcoholwith beryllium nitrate in an amount ranging from about A; to 10% by weight of the polyvinyl alcohol and treating the mixture with a water soluble inorganic basic material.

6. The process of producing a light sensitive photographic element comprising a silver halide uniformly dispersed in a tough, colorless gel of polyvinyl alcohol which comprises adding to an aqueous solution of polyvinyl alcohol, an alkali metal halide, adding silver nitrate while continuously stirring the mass, incorporating a water soluble inorganic beryllium salt in a gelling amount, coating the composition on a support and treating it with ammonia.

7. The process as defined in claim 4, wherein the berryllium salt is beryllium nitrate.

8. The process as defined in claim 4, wherein the beryllium salt is beryllium bromide.

9. The product of the process of claim 1.

10. The product of the process of claim 2.

11. The product of the process of claim 4.

12. The product of the process of claim 6.

13. The product of the process of claim 6.

DONALD E. SARGENT. JOHN C. BAILAR, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,412,200 Blum Dec. 10, 1946 2,439,108 Staehle Apr. 6, 1948 OTHER REFERENCES PVA Publication, Dupont R 8: H Technical Bulletin, 7 pp., copyright 1940, page 3 cited. 

1. THE METHOD OF PREPARING A TOUGH, COLORLESS GEL WHICH COMPRISES MIXING AN AQUEOUS SOLUTION OF POLYVINYL ALCOHOL WITH A WATER SOLUBLE INORGANIC BERYLLIUM SALT IN A GELLING AMOUNT AND TREATING THE MIXTURE WITH A WATER SOLUBLE INORGANIC BASIC MATERIAL.
 6. THE PROCESS OF PRODUCING A LIGHT SENSITIVE PHOTOGRAPHIC ELEMENT COMPRISING A SILVER HALIDE UNIFORMLY DISPERSED IN A TOUGH, COLORLESS GEL OF POLYVINYL ALCOHOL WHICH COMPRISES ADDING TO AN AQUEOUS SOLUTION OF POLYVINYL ALCOHOL, AN ALKALI METAL HALIDE, ADDING SILVER NITRATE WHILE CONTINUOUSLY STIRRING THE MASS, INCORPORATING A WATER SOLUBLE INORGANIC BERYLLIUM SALT IN A GELLING AMOUNT, COATING THE COMPOSITION ON A SUPPORT AND TREATING IT WITH AMMONIA. 